As a rack and pinion gear mechanism in the prior art technology, it is well known, for example, that is disclosed in Japanese Laid Open Patent Sho 63-176857 patent gazette.
FIG. 1 is a front view to show a constitution of the rack and pinion gear mechanism in the prior art technology which is disclosed in the above mentioned Laid Open patent gazette. In the drawing a reference numeral 1 designates a main body rack, 2 designates a conveying means to carry pinion series 3A, 3B, 3C and the like. The main body rack 1 is fixed on the main body flame by pins 5 and 6. In a pinion introducing side (which is shown as right side in FIG. 1) of the main body rack 1, a introducing segment rack 7 is arranged capable of rocking in vertical direction around a pin 6 as an axis contacting with the main body rack 1. At a junction point 8 of an end portion of the main body rack 1 and an end portion 7A of the introducing segment rack 7, a pitch line 11 in tooth depth direction of the introducing segment rack 7 and a pitch line 13 in tooth depth direction of the main body 1 are matched. And the introducing segment rack 7 is arranged in relation to the main body rack 1 such that a gear pitch 9 of the introducing segment rack 7 at the junction point 8 is made aligned with a gear pitch 10 of the main body rack 1. An end portion 7B of the pinion introducing side of introducing segment rack 7 is held so that the pitch line 11 in tooth depth direction becomes at least lower than the pitch line 13 of tooth depth direction of the main body rack 1 in a predetermined amount 12. At this point the above mentioned amount 12 is maintained by means that a block 15 which is built as one body in the introducing segment rack 7 is pushed against a stop pin 14 by a boost up force of spring 16.
And a distance 20 between the stop pin 14 and an end surface of the end portion 7B of pinion introducing side of the introducing segment rack 7 is set less than one half of the gear pitch. The spring 17 is an elastic member to press the introducing segment rack 7 to the main body rack 1. A force generated in a tooth surfaces when the introducing segment rack 7 and the pinion 3B and the like are engaged, can be absorbed by a displacement and its return in longitudinal direction of the introducing segment rack 7.
Hereinafter operation of the mechanism will be explained.
When the pinion 3B, for example, usually comes from right hand direction of the drawing and arrives on the introducing segment rack 7, a tooth point of the pinion 3B and a tooth point of the introducing segment rack 7 interfere together. At this point the introducing segment rack 7 rocks downward around axis of the pin 6 as a center to absorb the force generated at the tooth points. By this movement disadvantages such as a malfunction of the gear mechanism, a damage of driving motor, a breakage of teeth and the like are prevented.
However in the rack and pinion gear mechanism in the prior art technology there has been a problem that a constitution of the gear mechanism is too complicated because a means to prevent the disadvantages which is generated by a confliction of the tooth points, is composed of the introducing segment rack 7 that moves to a direction to release an engagement when the confliction of tooth points occurs, the spring 16 that always presses the introducing segment rack 7 upward to hold it at a predetermined position and the spring 17 that urges the gears in a direction for the engagement and makes the gears smoothly engaged when the engagement is released.
The present invention has been made to solve the above described problem and it is an object of the invention to provide a rack and pinion gear mechanism by which the disadvantages caused by confliction of the tooth points can be prevented with a simple constitution.